This research is directed toward obtaining basic biochemical information on the genetic mechanism involved in changes of concentration of specific cytochrome P-450 species in Drosophila. The hemoproteins will be solubilized and purified from wild-type and mutant stocks of Drosophila melanogaster and used as markers for cytochrome P-450 phenotype by SDS-polyacrylamide gel electrophoresis. The site of genetic control will be sought by crosses to stocks with marked inversions to all chromosomes and the usual scheme for making all possible homozygous combinations of wild-type chromosomes. It is hoped that the results will provide a better understanding of the phenomenon of insecticide resistance and will serve as a basis for studies on mutagenicity by chemicals in Drosophila.